// Copyright 2017-2019 Parity Technologies (UK) Ltd.
// This file is part of Substrate.

// Substrate is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Substrate is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.

//! Primitives for the runtime modules.

use rstd::prelude::*;
use rstd::{self, result, marker::PhantomData, convert::{TryFrom, TryInto}};
use runtime_io;
#[cfg(feature = "std")] use std::fmt::{Debug, Display};
#[cfg(feature = "std")] use serde::{Serialize, Deserialize, de::DeserializeOwned};
use substrate_primitives::{self, Hasher, Blake2Hasher};
use crate::codec::{Codec, Encode, Decode, HasCompact};
use crate::transaction_validity::TransactionValidity;
use crate::generic::{Digest, DigestItem};
pub use integer_sqrt::IntegerSquareRoot;
pub use num_traits::{
	Zero, One, Bounded, CheckedAdd, CheckedSub, CheckedMul, CheckedDiv,
	CheckedShl, CheckedShr
};
use rstd::ops::{
	Add, Sub, Mul, Div, Rem, AddAssign, SubAssign, MulAssign, DivAssign,
	RemAssign, Shl, Shr
};

/// A lazy value.
pub trait Lazy<T: ?Sized> {
	/// Get a reference to the underlying value.
	///
	/// This will compute the value if the function is invoked for the first time.
	fn get(&mut self) -> &T;
}

impl<'a> Lazy<[u8]> for &'a [u8] {
	fn get(&mut self) -> &[u8] { &**self }
}

/// Means of signature verification.
pub trait Verify {
	/// Type of the signer.
	type Signer;
	/// Verify a signature. Return `true` if signature is valid for the value.
	fn verify<L: Lazy<[u8]>>(&self, msg: L, signer: &Self::Signer) -> bool;
}

impl Verify for substrate_primitives::ed25519::Signature {
	type Signer = substrate_primitives::ed25519::Public;
	fn verify<L: Lazy<[u8]>>(&self, mut msg: L, signer: &Self::Signer) -> bool {
		runtime_io::ed25519_verify(self.as_ref(), msg.get(), signer)
	}
}

impl Verify for substrate_primitives::sr25519::Signature {
	type Signer = substrate_primitives::sr25519::Public;
	fn verify<L: Lazy<[u8]>>(&self, mut msg: L, signer: &Self::Signer) -> bool {
		runtime_io::sr25519_verify(self.as_ref(), msg.get(), signer)
	}
}

/// Some sort of check on the origin is performed by this object.
pub trait EnsureOrigin<OuterOrigin> {
	/// A return type.
	type Success;
	/// Perform the origin check.
	fn ensure_origin(o: OuterOrigin) -> result::Result<Self::Success, &'static str> {
		Self::try_origin(o).map_err(|_| "Invalid origin")
	}
	/// Perform the origin check.
	fn try_origin(o: OuterOrigin) -> result::Result<Self::Success, OuterOrigin>;
}

/// Means of changing one type into another in a manner dependent on the source type.
pub trait Lookup {
	/// Type to lookup from.
	type Source;
	/// Type to lookup into.
	type Target;
	/// Attempt a lookup.
	fn lookup(&self, s: Self::Source) -> result::Result<Self::Target, &'static str>;
}

/// Means of changing one type into another in a manner dependent on the source type.
/// This variant is different to `Lookup` in that it doesn't (can cannot) require any
/// context.
pub trait StaticLookup {
	/// Type to lookup from.
	type Source: Codec + Clone + PartialEq + MaybeDebug;
	/// Type to lookup into.
	type Target;
	/// Attempt a lookup.
	fn lookup(s: Self::Source) -> result::Result<Self::Target, &'static str>;
	/// Convert from Target back to Source.
	fn unlookup(t: Self::Target) -> Self::Source;
}

/// A lookup implementation returning the input value.
#[derive(Default)]
pub struct IdentityLookup<T>(PhantomData<T>);
impl<T: Codec + Clone + PartialEq + MaybeDebug> StaticLookup for IdentityLookup<T> {
	type Source = T;
	type Target = T;
	fn lookup(x: T) -> result::Result<T, &'static str> { Ok(x) }
	fn unlookup(x: T) -> T { x }
}
impl<T> Lookup for IdentityLookup<T> {
	type Source = T;
	type Target = T;
	fn lookup(&self, x: T) -> result::Result<T, &'static str> { Ok(x) }
}

/// Get the "current" block number.
pub trait CurrentHeight {
	/// The type of the block number.
	type BlockNumber;

	/// Return the current block number. Not allowed to fail.
	fn current_height(&self) -> Self::BlockNumber;
}

/// Translate a block number into a hash.
pub trait BlockNumberToHash {
	/// The type of the block number.
	type BlockNumber: Zero;

	/// The type of the hash.
	type Hash: Encode;

	/// Get the hash for a given block number, or `None` if unknown.
	fn block_number_to_hash(&self, n: Self::BlockNumber) -> Option<Self::Hash>;

	/// Get the genesis block hash; this should always be known.
	fn genesis_hash(&self) -> Self::Hash {
		self.block_number_to_hash(Zero::zero()).expect("All blockchains must know their genesis block hash; qed")
	}
}

/// Extensible conversion trait. Generic over both source and destination types.
pub trait Convert<A, B> {
	/// Make conversion.
	fn convert(a: A) -> B;
}

impl<A, B: Default> Convert<A, B> for () {
	fn convert(_: A) -> B { Default::default() }
}

/// A structure that performs identity conversion.
pub struct Identity;
impl<T> Convert<T, T> for Identity {
	fn convert(a: T) -> T { a }
}

/// A meta trait for arithmetic.
///
/// Arithmetic types do all the usual stuff you'd expect numbers to do. They are guaranteed to
/// be able to represent at least `u32` values without loss, hence the trait implies `From<u32>`
/// and smaller ints. All other conversions are fallible.
pub trait SimpleArithmetic:
	Zero + One + IntegerSquareRoot +
	From<u8> + From<u16> + From<u32> + TryInto<u8> + TryInto<u16> + TryInto<u32> +
	TryFrom<u64> + TryInto<u64> + TryFrom<u128> + TryInto<u128> + TryFrom<usize> + TryInto<usize> +
	UniqueSaturatedInto<u8> + UniqueSaturatedInto<u16> + UniqueSaturatedInto<u32> +
	UniqueSaturatedFrom<u64> + UniqueSaturatedInto<u64> + UniqueSaturatedFrom<u128> + UniqueSaturatedInto<u128> +
	Add<Self, Output = Self> + AddAssign<Self> +
	Sub<Self, Output = Self> + SubAssign<Self> +
	Mul<Self, Output = Self> + MulAssign<Self> +
	Div<Self, Output = Self> + DivAssign<Self> +
	Rem<Self, Output = Self> + RemAssign<Self> +
	Shl<u32, Output = Self> + Shr<u32, Output = Self> +
	CheckedShl + CheckedShr + CheckedAdd + CheckedSub + CheckedMul + CheckedDiv +
	Saturating + PartialOrd<Self> + Ord + Bounded +
	HasCompact + Sized
{}
impl<T:
	Zero + One + IntegerSquareRoot +
	From<u8> + From<u16> + From<u32> + TryInto<u8> + TryInto<u16> + TryInto<u32> +
	TryFrom<u64> + TryInto<u64> + TryFrom<u128> + TryInto<u128> + TryFrom<usize> + TryInto<usize> +
	UniqueSaturatedInto<u8> + UniqueSaturatedInto<u16> + UniqueSaturatedInto<u32> +
	UniqueSaturatedFrom<u64> + UniqueSaturatedInto<u64> + UniqueSaturatedFrom<u128> +
	UniqueSaturatedInto<u128> + UniqueSaturatedFrom<usize> + UniqueSaturatedInto<usize> +
	Add<Self, Output = Self> + AddAssign<Self> +
	Sub<Self, Output = Self> + SubAssign<Self> +
	Mul<Self, Output = Self> + MulAssign<Self> +
	Div<Self, Output = Self> + DivAssign<Self> +
	Rem<Self, Output = Self> + RemAssign<Self> +
	Shl<u32, Output = Self> + Shr<u32, Output = Self> +
	CheckedShl + CheckedShr + CheckedAdd + CheckedSub + CheckedMul + CheckedDiv +
	Saturating + PartialOrd<Self> + Ord + Bounded +
	HasCompact + Sized
> SimpleArithmetic for T {}

/// Just like `From` except that if the source value is too big to fit into the destination type
/// then it'll saturate the destination.
pub trait UniqueSaturatedFrom<T: Sized>: Sized {
	/// Convert from a value of `T` into an equivalent instance of `Self`.
	fn unique_saturated_from(t: T) -> Self;
}

/// Just like `Into` except that if the source value is too big to fit into the destination type
/// then it'll saturate the destination.
pub trait UniqueSaturatedInto<T: Sized>: Sized {
	/// Consume self to return an equivalent value of `T`.
	fn unique_saturated_into(self) -> T;
}

impl<T: Sized, S: TryFrom<T> + Bounded + Sized> UniqueSaturatedFrom<T> for S {
	fn unique_saturated_from(t: T) -> Self {
		S::try_from(t).unwrap_or_else(|_| Bounded::max_value())
	}
}

impl<T: Bounded + Sized, S: TryInto<T> + Sized> UniqueSaturatedInto<T> for S {
	fn unique_saturated_into(self) -> T {
		self.try_into().unwrap_or_else(|_| Bounded::max_value())
	}
}

/// Simple trait to use checked mul and max value to give a saturated mul operation over
/// supported types.
pub trait Saturating {
	/// Saturated addition - if the product can't fit in the type then just use max-value.
	fn saturating_add(self, o: Self) -> Self;

	/// Saturated subtraction - if the product can't fit in the type then just use max-value.
	fn saturating_sub(self, o: Self) -> Self;

	/// Saturated multiply - if the product can't fit in the type then just use max-value.
	fn saturating_mul(self, o: Self) -> Self;
}

impl<T: CheckedMul + Bounded + num_traits::Saturating> Saturating for T {
	fn saturating_add(self, o: Self) -> Self {
		<Self as num_traits::Saturating>::saturating_add(self, o)
	}
	fn saturating_sub(self, o: Self) -> Self {
		<Self as num_traits::Saturating>::saturating_sub(self, o)
	}
	fn saturating_mul(self, o: Self) -> Self {
		self.checked_mul(&o).unwrap_or_else(Bounded::max_value)
	}
}

/// Convenience type to work around the highly unergonomic syntax needed
/// to invoke the functions of overloaded generic traits, in this case
/// `SaturatedFrom` and `SaturatedInto`.
pub trait SaturatedConversion {
	/// Convert from a value of `T` into an equivalent instance of `Self`.
	///
	/// This just uses `UniqueSaturatedFrom` internally but with this
	/// variant you can provide the destination type using turbofish syntax
	/// in case Rust happens not to assume the correct type.
	fn saturated_from<T>(t: T) -> Self where Self: UniqueSaturatedFrom<T> {
		<Self as UniqueSaturatedFrom<T>>::unique_saturated_from(t)
	}

	/// Consume self to return an equivalent value of `T`.
	///
	/// This just uses `UniqueSaturatedInto` internally but with this
	/// variant you can provide the destination type using turbofish syntax
	/// in case Rust happens not to assume the correct type.
	fn saturated_into<T>(self) -> T where Self: UniqueSaturatedInto<T> {
		<Self as UniqueSaturatedInto<T>>::unique_saturated_into(self)
	}
}
impl<T: Sized> SaturatedConversion for T {}

/// Convenience type to work around the highly unergonomic syntax needed
/// to invoke the functions of overloaded generic traits, in this case
/// `TryFrom` and `TryInto`.
pub trait CheckedConversion {
	/// Convert from a value of `T` into an equivalent instance of `Option<Self>`.
	///
	/// This just uses `TryFrom` internally but with this
	/// variant you can provide the destination type using turbofish syntax
	/// in case Rust happens not to assume the correct type.
	fn checked_from<T>(t: T) -> Option<Self> where Self: TryFrom<T> {
		<Self as TryFrom<T>>::try_from(t).ok()
	}
	/// Consume self to return `Some` equivalent value of `Option<T>`.
	///
	/// This just uses `TryInto` internally but with this
	/// variant you can provide the destination type using turbofish syntax
	/// in case Rust happens not to assume the correct type.
	fn checked_into<T>(self) -> Option<T> where Self: TryInto<T> {
		<Self as TryInto<T>>::try_into(self).ok()
	}
}
impl<T: Sized> CheckedConversion for T {}

/// Trait for things that can be clear (have no bits set). For numeric types, essentially the same
/// as `Zero`.
pub trait Clear {
	/// True iff no bits are set.
	fn is_clear(&self) -> bool;

	/// Return the value of Self that is clear.
	fn clear() -> Self;
}

impl<T: Default + Eq + PartialEq> Clear for T {
	fn is_clear(&self) -> bool { *self == Self::clear() }
	fn clear() -> Self { Default::default() }
}

/// A meta trait for all bit ops.
pub trait SimpleBitOps:
	Sized + Clear +
	rstd::ops::BitOr<Self, Output = Self> +
	rstd::ops::BitXor<Self, Output = Self> +
	rstd::ops::BitAnd<Self, Output = Self>
{}
impl<T:
	Sized + Clear +
	rstd::ops::BitOr<Self, Output = Self> +
	rstd::ops::BitXor<Self, Output = Self> +
	rstd::ops::BitAnd<Self, Output = Self>
> SimpleBitOps for T {}

/// The block finalization trait. Implementing this lets you express what should happen
/// for your module when the block is ending.
pub trait OnFinalize<BlockNumber> {
	/// The block is being finalized. Implement to have something happen.
	fn on_finalize(_n: BlockNumber) {}
}

impl<N> OnFinalize<N> for () {}

/// The block initialization trait. Implementing this lets you express what should happen
/// for your module when the block is beginning (right before the first extrinsic is executed).
pub trait OnInitialize<BlockNumber> {
	/// The block is being initialized. Implement to have something happen.
	fn on_initialize(_n: BlockNumber) {}
}

impl<N> OnInitialize<N> for () {}

/// Off-chain computation trait.
///
/// Implementing this trait on a module allows you to perform long-running tasks
/// that make validators generate extrinsics (either transactions or inherents)
/// with the results of those long-running computations.
///
/// NOTE: This function runs off-chain, so it can access the block state,
/// but cannot preform any alterations.
pub trait OffchainWorker<BlockNumber> {
	/// This function is being called on every block.
	///
	/// Implement this and use special `extern`s to generate transactions or inherents.
	/// Any state alterations are lost and are not persisted.
	fn generate_extrinsics(_n: BlockNumber) {}
}

impl<N> OffchainWorker<N> for () {}

macro_rules! tuple_impl {
	($first:ident, $($rest:ident,)+) => {
		tuple_impl!([$first] [$first] [$($rest)+]);
	};
	([$($direct:ident)+] [$($reverse:ident)+] []) => {
		impl<
			Number: Copy,
			$($direct: OnFinalize<Number>),+
		> OnFinalize<Number> for ($($direct),+,) {
			fn on_finalize(n: Number) {
				$($reverse::on_finalize(n);)+
			}
		}
		impl<
			Number: Copy,
			$($direct: OnInitialize<Number>),+
		> OnInitialize<Number> for ($($direct),+,) {
			fn on_initialize(n: Number) {
				$($direct::on_initialize(n);)+
			}
		}
		impl<
			Number: Copy,
			$($direct: OffchainWorker<Number>),+
		> OffchainWorker<Number> for ($($direct),+,) {
			fn generate_extrinsics(n: Number) {
				$($direct::generate_extrinsics(n);)+
			}
		}
	};
	([$($direct:ident)+] [$($reverse:ident)+] [$first:ident $($rest:ident)*]) => {
		tuple_impl!([$($direct)+] [$($reverse)+] []);
		tuple_impl!([$($direct)+ $first] [$first $($reverse)+] [$($rest)*]);
	};
}

#[allow(non_snake_case)]
tuple_impl!(A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z,);

/// Abstraction around hashing
pub trait Hash: 'static + MaybeSerializeDebug + Clone + Eq + PartialEq {	// Stupid bug in the Rust compiler believes derived
																	// traits must be fulfilled by all type parameters.
	/// The hash type produced.
	type Output: Member + MaybeSerializeDebug + rstd::hash::Hash + AsRef<[u8]> + AsMut<[u8]> + Copy
		+ Default + Encode + Decode;

	/// The associated hash_db Hasher type.
	type Hasher: Hasher<Out=Self::Output>;

	/// Produce the hash of some byte-slice.
	fn hash(s: &[u8]) -> Self::Output;

	/// Produce the hash of some codec-encodable value.
	fn hash_of<S: Codec>(s: &S) -> Self::Output {
		Encode::using_encoded(s, Self::hash)
	}

	/// Produce the trie-db root of a mapping from indices to byte slices.
	fn enumerated_trie_root(items: &[&[u8]]) -> Self::Output;

	/// Iterator-based version of `enumerated_trie_root`.
	fn ordered_trie_root<
		I: IntoIterator<Item = A> + Iterator<Item = A>,
		A: AsRef<[u8]>
	>(input: I) -> Self::Output;

	/// The Patricia tree root of the given mapping as an iterator.
	fn trie_root<
		I: IntoIterator<Item = (A, B)>,
		A: AsRef<[u8]> + Ord,
		B: AsRef<[u8]>
	>(input: I) -> Self::Output;

	/// Acquire the global storage root.
	fn storage_root() -> Self::Output;

	/// Acquire the global storage changes root.
	fn storage_changes_root(parent_hash: Self::Output) -> Option<Self::Output>;
}

/// Blake2-256 Hash implementation.
#[derive(PartialEq, Eq, Clone)]
#[cfg_attr(feature = "std", derive(Debug, Serialize, Deserialize))]
pub struct BlakeTwo256;

impl Hash for BlakeTwo256 {
	type Output = substrate_primitives::H256;
	type Hasher = Blake2Hasher;
	fn hash(s: &[u8]) -> Self::Output {
		runtime_io::blake2_256(s).into()
	}
	fn enumerated_trie_root(items: &[&[u8]]) -> Self::Output {
		runtime_io::enumerated_trie_root::<Blake2Hasher>(items).into()
	}
	fn trie_root<
		I: IntoIterator<Item = (A, B)>,
		A: AsRef<[u8]> + Ord,
		B: AsRef<[u8]>
	>(input: I) -> Self::Output {
		runtime_io::trie_root::<Blake2Hasher, _, _, _>(input).into()
	}
	fn ordered_trie_root<
		I: IntoIterator<Item = A> + Iterator<Item = A>,
		A: AsRef<[u8]>
	>(input: I) -> Self::Output {
		runtime_io::ordered_trie_root::<Blake2Hasher, _, _>(input).into()
	}
	fn storage_root() -> Self::Output {
		runtime_io::storage_root().into()
	}
	fn storage_changes_root(parent_hash: Self::Output) -> Option<Self::Output> {
		runtime_io::storage_changes_root(parent_hash.into()).map(Into::into)
	}
}

/// Something that can be checked for equality and printed out to a debug channel if bad.
pub trait CheckEqual {
	/// Perform the equality check.
	fn check_equal(&self, other: &Self);
}

impl CheckEqual for substrate_primitives::H256 {
	#[cfg(feature = "std")]
	fn check_equal(&self, other: &Self) {
		use substrate_primitives::hexdisplay::HexDisplay;
		if self != other {
			println!("Hash: given={}, expected={}", HexDisplay::from(self.as_fixed_bytes()), HexDisplay::from(other.as_fixed_bytes()));
		}
	}

	#[cfg(not(feature = "std"))]
	fn check_equal(&self, other: &Self) {
		if self != other {
			runtime_io::print("Hash not equal");
			runtime_io::print(self.as_bytes());
			runtime_io::print(other.as_bytes());
		}
	}
}

impl<H: PartialEq + Eq + MaybeDebug> CheckEqual for super::generic::DigestItem<H> where H: Encode {
	#[cfg(feature = "std")]
	fn check_equal(&self, other: &Self) {
		if self != other {
			println!("DigestItem: given={:?}, expected={:?}", self, other);
		}
	}

	#[cfg(not(feature = "std"))]
	fn check_equal(&self, other: &Self) {
		if self != other {
			runtime_io::print("DigestItem not equal");
			runtime_io::print(&Encode::encode(self)[..]);
			runtime_io::print(&Encode::encode(other)[..]);
		}
	}
}

/// A type that implements Serialize and Debug when in std environment.
#[cfg(feature = "std")]
pub trait MaybeSerializeDebugButNotDeserialize: Serialize + Debug {}
#[cfg(feature = "std")]
impl<T: Serialize + Debug> MaybeSerializeDebugButNotDeserialize for T {}

/// A type that implements Serialize and Debug when in std environment.
#[cfg(not(feature = "std"))]
pub trait MaybeSerializeDebugButNotDeserialize {}
#[cfg(not(feature = "std"))]
impl<T> MaybeSerializeDebugButNotDeserialize for T {}

/// A type that implements Serialize when in std environment.
#[cfg(feature = "std")]
pub trait MaybeSerialize: Serialize {}
#[cfg(feature = "std")]
impl<T: Serialize> MaybeSerialize for T {}

/// A type that implements Serialize when in std environment.
#[cfg(not(feature = "std"))]
pub trait MaybeSerialize {}
#[cfg(not(feature = "std"))]
impl<T> MaybeSerialize for T {}

/// A type that implements Serialize, DeserializeOwned and Debug when in std environment.
#[cfg(feature = "std")]
pub trait MaybeSerializeDebug: Serialize + DeserializeOwned + Debug {}
#[cfg(feature = "std")]
impl<T: Serialize + DeserializeOwned + Debug> MaybeSerializeDebug for T {}

/// A type that implements Serialize, DeserializeOwned and Debug when in std environment.
#[cfg(not(feature = "std"))]
pub trait MaybeSerializeDebug {}
#[cfg(not(feature = "std"))]
impl<T> MaybeSerializeDebug for T {}

/// A type that implements Debug when in std environment.
#[cfg(feature = "std")]
pub trait MaybeDebug: Debug {}
#[cfg(feature = "std")]
impl<T: Debug> MaybeDebug for T {}

/// A type that implements Debug when in std environment.
#[cfg(not(feature = "std"))]
pub trait MaybeDebug {}
#[cfg(not(feature = "std"))]
impl<T> MaybeDebug for T {}

/// A type that implements Display when in std environment.
#[cfg(feature = "std")]
pub trait MaybeDisplay: Display {}
#[cfg(feature = "std")]
impl<T: Display> MaybeDisplay for T {}

/// A type that implements Display when in std environment.
#[cfg(not(feature = "std"))]
pub trait MaybeDisplay {}
#[cfg(not(feature = "std"))]
impl<T> MaybeDisplay for T {}

/// A type that implements Hash when in std environment.
#[cfg(feature = "std")]
pub trait MaybeHash: ::rstd::hash::Hash {}
#[cfg(feature = "std")]
impl<T: ::rstd::hash::Hash> MaybeHash for T {}

/// A type that implements Hash when in std environment.
#[cfg(not(feature = "std"))]
pub trait MaybeHash {}
#[cfg(not(feature = "std"))]
impl<T> MaybeHash for T {}

/// A type that provides a randomness beacon.
pub trait RandomnessBeacon {
	/// Returns 32 bytes of random data. The output will change eventually, but
	/// is not guaranteed to be different between any two calls.
	///
	/// # Security
	///
	/// This MUST NOT be used for gambling, as it can be influenced by a
	/// malicious validator in the short term.  It MAY be used in many
	/// cryptographic protocols, however, so long as one remembers that this
	/// (like everything else on-chain) is public.  For example, it can be
	/// used where a number is needed that cannot have been chosen by an
	/// adversary, for purposes such as public-coin zero-knowledge proofs.
	fn random() -> [u8; 32];
}

/// A type that can be used in runtime structures.
pub trait Member: Send + Sync + Sized + MaybeDebug + Eq + PartialEq + Clone + 'static {}
impl<T: Send + Sync + Sized + MaybeDebug + Eq + PartialEq + Clone + 'static> Member for T {}

/// Something which fulfills the abstract idea of a Substrate header. It has types for a `Number`,
/// a `Hash` and a `Digest`. It provides access to an `extrinsics_root`, `state_root` and
/// `parent_hash`, as well as a `digest` and a block `number`.
///
/// You can also create a `new` one from those fields.
pub trait Header: Clone + Send + Sync + Codec + Eq + MaybeSerializeDebugButNotDeserialize + 'static {
	/// Header number.
	type Number: Member + MaybeSerializeDebug + ::rstd::hash::Hash + Copy + MaybeDisplay + SimpleArithmetic + Codec;
	/// Header hash type
	type Hash: Member + MaybeSerializeDebug + ::rstd::hash::Hash + Copy + MaybeDisplay + Default + SimpleBitOps + Codec + AsRef<[u8]> + AsMut<[u8]>;
	/// Hashing algorithm
	type Hashing: Hash<Output = Self::Hash>;

	/// Creates new header.
	fn new(
		number: Self::Number,
		extrinsics_root: Self::Hash,
		state_root: Self::Hash,
		parent_hash: Self::Hash,
		digest: Digest<Self::Hash>,
	) -> Self;

	/// Returns a reference to the header number.
	fn number(&self) -> &Self::Number;
	/// Sets the header number.
	fn set_number(&mut self, number: Self::Number);

	/// Returns a reference to the extrinsics root.
	fn extrinsics_root(&self) -> &Self::Hash;
	/// Sets the extrinsic root.
	fn set_extrinsics_root(&mut self, root: Self::Hash);

	/// Returns a reference to the state root.
	fn state_root(&self) -> &Self::Hash;
	/// Sets the state root.
	fn set_state_root(&mut self, root: Self::Hash);

	/// Returns a reference to the parent hash.
	fn parent_hash(&self) -> &Self::Hash;
	/// Sets the parent hash.
	fn set_parent_hash(&mut self, hash: Self::Hash);

	/// Returns a reference to the digest.
	fn digest(&self) -> &Digest<Self::Hash>;
	/// Get a mutable reference to the digest.
	fn digest_mut(&mut self) -> &mut Digest<Self::Hash>;

	/// Returns the hash of the header.
	fn hash(&self) -> Self::Hash {
		<Self::Hashing as Hash>::hash_of(self)
	}
}

/// Something which fulfills the abstract idea of a Substrate block. It has types for an
/// `Extrinsic` piece of information as well as a `Header`.
///
/// You can get an iterator over each of the `extrinsics` and retrieve the `header`.
pub trait Block: Clone + Send + Sync + Codec + Eq + MaybeSerializeDebugButNotDeserialize + 'static {
	/// Type of extrinsics.
	type Extrinsic: Member + Codec + Extrinsic + MaybeSerialize;
	/// Header type.
	type Header: Header<Hash=Self::Hash>;
	/// Block hash type.
	type Hash: Member + MaybeSerializeDebug + ::rstd::hash::Hash + Copy + MaybeDisplay + Default + SimpleBitOps + Codec + AsRef<[u8]> + AsMut<[u8]>;

	/// Returns a reference to the header.
	fn header(&self) -> &Self::Header;
	/// Returns a reference to the list of extrinsics.
	fn extrinsics(&self) -> &[Self::Extrinsic];
	/// Split the block into header and list of extrinsics.
	fn deconstruct(self) -> (Self::Header, Vec<Self::Extrinsic>);
	/// Creates new block from header and extrinsics.
	fn new(header: Self::Header, extrinsics: Vec<Self::Extrinsic>) -> Self;
	/// Returns the hash of the block.
	fn hash(&self) -> Self::Hash {
		<<Self::Header as Header>::Hashing as Hash>::hash_of(self.header())
	}
}

/// Something that acts like an `Extrinsic`.
pub trait Extrinsic {
	/// Is this `Extrinsic` signed?
	/// If no information are available about signed/unsigned, `None` should be returned.
	fn is_signed(&self) -> Option<bool> { None }
}

/// Extract the hashing type for a block.
pub type HashFor<B> = <<B as Block>::Header as Header>::Hashing;
/// Extract the number type for a block.
pub type NumberFor<B> = <<B as Block>::Header as Header>::Number;
/// Extract the digest type for a block.
pub type DigestFor<B> = Digest<<<B as Block>::Header as Header>::Hash>;
/// Extract the digest item type for a block.
pub type DigestItemFor<B> = DigestItem<<<B as Block>::Header as Header>::Hash>;

/// A "checkable" piece of information, used by the standard Substrate Executive in order to
/// check the validity of a piece of extrinsic information, usually by verifying the signature.
/// Implement for pieces of information that require some additional context `Context` in order to be
/// checked.
pub trait Checkable<Context>: Sized {
	/// Returned if `check` succeeds.
	type Checked;

	/// Check self, given an instance of Context.
	fn check(self, c: &Context) -> Result<Self::Checked, &'static str>;
}

/// A "checkable" piece of information, used by the standard Substrate Executive in order to
/// check the validity of a piece of extrinsic information, usually by verifying the signature.
/// Implement for pieces of information that don't require additional context in order to be
/// checked.
pub trait BlindCheckable: Sized {
	/// Returned if `check` succeeds.
	type Checked;

	/// Check self.
	fn check(self) -> Result<Self::Checked, &'static str>;
}

// Every `BlindCheckable` is also a `StaticCheckable` for arbitrary `Context`.
impl<T: BlindCheckable, Context> Checkable<Context> for T {
	type Checked = <Self as BlindCheckable>::Checked;
	fn check(self, _c: &Context) -> Result<Self::Checked, &'static str> {
		BlindCheckable::check(self)
	}
}

/// An "executable" piece of information, used by the standard Substrate Executive in order to
/// enact a piece of extrinsic information by marshalling and dispatching to a named function
/// call.
///
/// Also provides information on to whom this information is attributable and an index that allows
/// each piece of attributable information to be disambiguated.
pub trait Applyable: Sized + Send + Sync {
	/// Id of the account that is responsible for this piece of information (sender).
	type AccountId: Member + MaybeDisplay;
	/// Index allowing to disambiguate other `Applyable`s from the same `AccountId`.
	type Index: Member + MaybeDisplay + SimpleArithmetic;
	/// Function call.
	type Call: Member;
	/// Returns a reference to the index if any.
	fn index(&self) -> Option<&Self::Index>;
	/// Returns a reference to the sender if any.
	fn sender(&self) -> Option<&Self::AccountId>;
	/// Deconstructs into function call and sender.
	fn deconstruct(self) -> (Self::Call, Option<Self::AccountId>);
}

/// Auxiliary wrapper that holds an api instance and binds it to the given lifetime.
pub struct ApiRef<'a, T>(T, rstd::marker::PhantomData<&'a ()>);

impl<'a, T> From<T> for ApiRef<'a, T> {
	fn from(api: T) -> Self {
		ApiRef(api, Default::default())
	}
}

impl<'a, T> rstd::ops::Deref for ApiRef<'a, T> {
	type Target = T;

	fn deref(&self) -> &Self::Target {
		&self.0
	}
}

impl<'a, T> rstd::ops::DerefMut for ApiRef<'a, T> {
	fn deref_mut(&mut self) -> &mut T {
		&mut self.0
	}
}

/// Something that provides a runtime api.
pub trait ProvideRuntimeApi {
	/// The concrete type that provides the api.
	type Api;

	/// Returns the runtime api.
	/// The returned instance will keep track of modifications to the storage. Any successful
	/// call to an api function, will `commit` its changes to an internal buffer. Otherwise,
	/// the modifications will be `discarded`. The modifications will not be applied to the
	/// storage, even on a `commit`.
	fn runtime_api<'a>(&'a self) -> ApiRef<'a, Self::Api>;
}

/// A marker trait for something that knows the type of the runtime block.
pub trait GetRuntimeBlockType {
	/// The `RuntimeBlock` type.
	type RuntimeBlock: self::Block;
}

/// A marker trait for something that knows the type of the node block.
pub trait GetNodeBlockType {
	/// The `NodeBlock` type.
	type NodeBlock: self::Block;
}

/// Something that provides information about a runtime api.
pub trait RuntimeApiInfo {
	/// The identifier of the runtime api.
	const ID: [u8; 8];
	/// The version of the runtime api.
	const VERSION: u32;
}

/// Something that can validate unsigned extrinsics.
pub trait ValidateUnsigned {
	/// The call to validate
	type Call;

	/// Return the validity of the call
	///
	/// This doesn't execute any side-effects; it merely checks
	/// whether the transaction would panic if it were included or not.
	///
	/// Changes made to storage should be discarded by caller.
	fn validate_unsigned(call: &Self::Call) -> TransactionValidity;
}

/// Opaque datatype that may be destructured into a series of raw byte slices (which represent
/// individual keys).
pub trait OpaqueKeys: Clone {
	/// Return the number of encoded keys.
	fn count() -> usize { 0 }
	/// Get the raw bytes of key with index `i`.
	fn get_raw(&self, i: usize) -> &[u8];
	/// Get the decoded key with index `i`.
	fn get<T: Decode>(&self, i: usize) -> Option<T> { T::decode(&mut self.get_raw(i)) }
	/// Verify a proof of ownership for the keys.
	fn ownership_proof_is_valid(&self, _proof: &[u8]) -> bool { true }
}

struct TrailingZeroInput<'a>(&'a [u8]);
impl<'a> codec::Input for TrailingZeroInput<'a> {
	fn read(&mut self, into: &mut [u8]) -> usize {
		let len = into.len().min(self.0.len());
		into[..len].copy_from_slice(&self.0[..len]);
		for i in &mut into[len..] {
			*i = 0;
		}
		self.0 = &self.0[len..];
		into.len()
	}
}

/// This type can be converted into and possibly from an AccountId (which itself is generic).
pub trait AccountIdConversion<AccountId>: Sized {
	/// Convert into an account ID. This is infallible.
	fn into_account(&self) -> AccountId;

	/// Try to convert an account ID into this type. Might not succeed.
	fn try_from_account(a: &AccountId) -> Option<Self>;
}

/// Provide a simply 4 byte identifier for a type.
pub trait TypeId {
	/// Simple 4 byte identifier.
	const TYPE_ID: [u8; 4];
}

/// Format is TYPE_ID ++ encode(parachain ID) ++ 00.... where 00... is indefinite trailing zeroes to fill AccountId.
impl<T: Encode + Decode + Default, Id: Encode + Decode + TypeId> AccountIdConversion<T> for Id {
	fn into_account(&self) -> T {
		(Id::TYPE_ID, self).using_encoded(|b|
			T::decode(&mut TrailingZeroInput(b))
		).unwrap_or_default()
	}

	fn try_from_account(x: &T) -> Option<Self> {
		x.using_encoded(|d| {
			if &d[0..4] != Id::TYPE_ID { return None }
			let mut cursor = &d[4..];
			let result = Decode::decode(&mut cursor)?;
			if cursor.iter().all(|x| *x == 0) {
				Some(result)
			} else {
				None
			}
		})
	}
}

#[cfg(test)]
mod tests {
	use super::AccountIdConversion;
	use crate::codec::{Encode, Decode};

	#[derive(Encode, Decode, Default, PartialEq, Debug)]
	struct U32Value(u32);
	impl super::TypeId for U32Value {
		const TYPE_ID: [u8; 4] = [0x0d, 0xf0, 0xfe, 0xca];
	}
	// cafef00d

	#[derive(Encode, Decode, Default, PartialEq, Debug)]
	struct U16Value(u16);
	impl super::TypeId for U16Value {
		const TYPE_ID: [u8; 4] = [0xfe, 0xca, 0x0d, 0xf0];
	}
	// f00dcafe

	type AccountId = u64;

	#[test]
	fn into_account_should_work() {
		let r: AccountId = U32Value::into_account(&U32Value(0xdeadbeef));
		assert_eq!(r, 0x_deadbeef_cafef00d);
	}

	#[test]
	fn try_from_account_should_work() {
		let r = U32Value::try_from_account(&0x_deadbeef_cafef00d_u64);
		assert_eq!(r.unwrap(), U32Value(0xdeadbeef));
	}

	#[test]
	fn into_account_with_fill_should_work() {
		let r: AccountId = U16Value::into_account(&U16Value(0xc0da));
		assert_eq!(r, 0x_0000_c0da_f00dcafe);
	}

	#[test]
	fn try_from_account_with_fill_should_work() {
		let r = U16Value::try_from_account(&0x0000_c0da_f00dcafe_u64);
		assert_eq!(r.unwrap(), U16Value(0xc0da));
	}

	#[test]
	fn bad_try_from_account_should_fail() {
		let r = U16Value::try_from_account(&0x0000_c0de_baadcafe_u64);
		assert!(r.is_none());
		let r = U16Value::try_from_account(&0x0100_c0da_f00dcafe_u64);
		assert!(r.is_none());
	}
}

/// Calls a given macro a number of times with a set of fixed params and an incrementing numeral.
/// e.g.
/// ```nocompile
/// count!(println ("{}",) foo, bar, baz);
/// // Will result in three `println!`s: "0", "1" and "2".
/// ```
#[macro_export]
macro_rules! count {
	($f:ident ($($x:tt)*) ) => ();
	($f:ident ($($x:tt)*) $x1:tt) => { $f!($($x)* 0); };
	($f:ident ($($x:tt)*) $x1:tt, $x2:tt) => { $f!($($x)* 0); $f!($($x)* 1); };
	($f:ident ($($x:tt)*) $x1:tt, $x2:tt, $x3:tt) => { $f!($($x)* 0); $f!($($x)* 1); $f!($($x)* 2); };
	($f:ident ($($x:tt)*) $x1:tt, $x2:tt, $x3:tt, $x4:tt) => {
		$f!($($x)* 0); $f!($($x)* 1); $f!($($x)* 2); $f!($($x)* 3);
	};
	($f:ident ($($x:tt)*) $x1:tt, $x2:tt, $x3:tt, $x4:tt, $x5:tt) => {
		$f!($($x)* 0); $f!($($x)* 1); $f!($($x)* 2); $f!($($x)* 3); $f!($($x)* 4);
	};
}

#[macro_export]
/// Just implement `OpaqueKeys` for a given tuple-struct.
/// Would be much nicer for this to be converted to `derive` code.
macro_rules! impl_opaque_keys {
	(
		pub struct $name:ident ( $( $t:ty ),* $(,)* );
	) => {
		impl_opaque_keys! {
			pub struct $name ( $( $t ,)* );
			impl OpaqueKeys for _ {}
		}
	};
	(
		pub struct $name:ident ( $( $t:ty ),* $(,)* );
		impl OpaqueKeys for _ {
			$($rest:tt)*
		}
	) => {
		#[derive(Default, Clone, PartialEq, Eq, $crate::codec::Encode, $crate::codec::Decode)]
		#[cfg_attr(feature = "std", derive(Debug, $crate::serde::Serialize, $crate::serde::Deserialize))]
		pub struct $name($( pub $t ,)*);
		impl $crate::traits::OpaqueKeys for $name {
			fn count() -> usize {
				let mut c = 0;
				$( let _: $t; c += 1; )*
				c
			}
			fn get_raw(&self, i: usize) -> &[u8] {
				$crate::count!(impl_opaque_keys (!! self i) $($t),*);
				&[]
			}
			$($rest)*
		}
	};
	( !! $self:ident $param_i:ident $i:tt) => {
		if $param_i == $i { return $self.$i.as_ref() }
	}
}